In order to calculate the actual flux of a luminaire we have to consider certain factors:
First of all, it is assumed that the real outdoor ambient temperature conditions are 35ºC. As a result, inside the luminaire the indoor temperature increases.
Secondly, we must bear in mind that with the luminaire in operation the Tj of the LED increases, being higher than the Tj25ºC that is obtained in the ideal conditions of a laboratory. Therefore, the flow of the LED (Φ LED) is lower.
Thirdly, we must consider the flux losses caused by the components of the luminaire themselves (optics, diffuser, closure…) as well as the thermal conditions inside the luminaire that reduce the flux emitted from the luminaire by up to 10%.
Once considering the three previous factors, to obtain the real efficiency of the luminaire we must use the following formula:
Where ΦLUMINARIA is the total flux emitted by the luminaire, measured in lumens (lm) and PLUM is the power of the sum of the LEDs + the driver in watts (W).